1. Field of the Invention
This invention relates to the production of inorganic peroxo compounds.
Inorganic peroxo compounds, particularly perborates, have long been used as oxidizing agents in bleaches, detergents and disinfectants. Whereas perborate tetrahydrate has hitherto mainly been used in detergents and bleaches, the monohydrate has also recently been acquiring increasing significance by virtue of its higher active oxygen content and its higher dissolving rate. According to present knowledge, these compounds are in reality the hexahydrate or rather the anhydrous form of cyclic sodium diperoxodiborate although the old names, perborate tetrahydrate (NaBO.sub.3.4 H.sub.2 O) and sodium perborate monohydrate (NaBO.sub.3.H.sub.2 O), are used in the following. The standard characterization based on the active oxygen content, according to which products containing more than 15% AO are termed monohydrate, is also retained in the following (theoretical active oxygen content of the monohydrate: 16.0% by weight).
2. Discussion of Related Art
In its production on an industrial scale from sodium borate and hydrogen peroxide, perborate tetrahydrate is generally obtained in the form of a coarsely crystalline, abrasion-resistant powder of relatively high apparent density. Accordingly, it can readily be incorporated in standard detergents. By contrast, perborate monohydrate, which is normally produced by drying from the perborate tetrahydrate, is a light porous material with little abrasion resistance which is difficult to incorporate in this form. Accordingly, there has been no shortage of attempts to eliminate these disadvantages of the monohydrate. One possibility in this regard is to granulate the perborate monohydrate. Thus, it is proposed in DE 26 50 225 to combine hydrogen peroxide and borate with simultaneous drying in a fluidized bed to form perborate monohydrate which accumulates in granular form providing the process is suitably managed. However, reliable adjustment of the process parameters is difficult. In other known processes, the tetrahydrate is first agglomerated with water and/or other granulation aids to form relatively large particles which are then dewatered in a following drying step to form perborate monohydrate granules (EP 202 519, Ep 295 950, EP 296 813 and earlier application DE-p 38 30 545.3 . One feature common to all these processes is that the granulated monohydrate is also obtained in a relatively light form, i.e. with a low apparent density. Accordingly, these forms of the monohydrate can only be used to a limited extent in modern detergents, which have very high apparent densities, because separation can occur. In addition, it is proposed in EP 102 419 to granulate perborates, particularly the oxoborate obtainable by heating of the monohydrate, by compaction. However, this process requires the addition of polytetrafluoroethylene as lubricant and gives a product unsuitable for detergents and bleaches, not the least because this additive is non-biodegradable.
Accordingly, the problem addressed by the present invention was to provide perborate monohydrate in a form suitable for use in modern detergents.